Organic pressure-sensitive adhesives have been finding increased utility principally to manufacture pressure sensitive adhesive tapes. For a variety of common uses, pressure-sensitive adhesive tapes manufactured with organic pressure-sensitive adhesives, have the requisite physical properties and low cost to make them very much in demand.
However, there are many uses for which pressure-sensitive tapes manufactured from organic pressure-sensitive adhesives are unsuitable. For example, organic pressure-sensitive adhesive tapes do not weather well. Such tapes have poor adhesive to low energy surfaces. These tapes have poor low temperature flexibility, and they have poor high temperature stability. Thus, organic pressure-sensitive adhesive tapes are generally unsuitable for use in outside graphics, such as striping on automobiles or graphics in windows; for use in bonding plastics and for use in conditions where temperature extremes are encountered.
Silicone pressure-sensitive adhesives are also well known adhesives and are widely employed in a variety of uses, including pressure-sensitive adhesive tape. Silicone pressure-sensitive adhesives exhibit excellent adhesion to very low energy surfaces, have excellent weatherability, are flexible at low temperature and are chemically stable at very high temperature. However, the principal drawback to a much wider spread use of silicone pressure-sensitive adhesives is cost.
Thus, the present day market in pressure-sensitive adhesives is split between high performance but costly silicone pressure-sensitive adhesives and organic pressure-sensitive adhesives which are cost effective for most uses. Of course, methods are known to obtain pressure-sensitive adhesives which have intermediate physical propterties as well as intermediate price.
One such method involves blending a solution of silicone pressure-sensitive adhesive and a solution of organic pressure-sensitive adhesive and applying the blend to a tape from solution. Another method disclosed in assignee's U.S. Pat. No. 4,791,163, hereby incorporated by reference, involves forming an emulsion of silicone pressure-sensitive adhesive and organic pressure-sensitive adhesive in water and applying the mixture to a tape from emulsion.
Although adhesives applied by these methods have substantially improved properties over organic adhesives, still certain properties can be further improved. For example, the shear strength of these adhesives is very poor, particularly under heat. This aspect is generally a feature of organic adhesives and is carried over into the organic/silicone adhesive composites.
It is an object of the present invention to manufacture silicone and organic pressure-sensitive adhesive composites with improved shear strength.